title: Viral distribution and life strategies in the Bach Dang Estuary, Vietnam.
abstract: Although the structure and dynamics of planktonic viruses in freshwater and seawater environments are relatively well documented, little is known about the occurrence and activity of these viruses in estuaries, especially in the tropics. Viral abundance, life strategies, and morphotype distribution were examined in the Bach Dang Estuary (Vietnam) during the dry season in 2009. The abundance of both viruses and their prokaryotic hosts decreased significantly from upstream to downstream, probably as the result of nutrient dilution and osmotic stress faced by the freshwater communities. The antibiotic mitomycin-C revealed that the fraction of lysogenic cells was substantially higher in the lower seawater part of the estuary (max 27.1%) than in the upper freshwater area where no inducible lysogens were observed. The question of whether there is a massive, continuous induction of marine lysogens caused by the mixing with freshwater is considered. Conversely, the production of lytic viruses declined as salinity increased, indicating a spatial succession of viral life strategies in this tropical estuary. Icosahedral tailless viruses with capsids smaller than 60 nm dominated the viral assemblage throughout the estuary (63.0% to 72.1% of the total viral counts), and their distribution was positively correlated with that of viral lytic production. Interestingly, the gamma-proteobacteria explained a significant portion of the variance in the <60 nm and 60 to 90 nm tailless viruses (92% and 80%, respectively), and in the Myoviridae (73%). Also, 60% of the variance of the tailless larger viruses (>90 nm) was explained by the beta-proteobacteria. Overall, these results support the view that the environment, through selection mechanisms, probably shapes the structure of the prokaryotic community. This might be in turn a source of selection for the virioplankton community via specific affiliation favoring particular morphotypes and life strategies.
authors.affiliation: UMR 5119, ECOSYM, Montpellier 2 University, CNRS, IRD, IFREMER, Montpellier, France. yvan.bettarel@ird.fr
authors.forename: Yvan
authors.initials: Y
authors.lastname: Bettarel
authors.forename: Thierry
authors.initials: T
authors.lastname: Bouvier
authors.forename: Martin
authors.initials: M
authors.lastname: Agis
authors.forename: Corinne
authors.initials: C
authors.lastname: Bouvier
authors.forename: Thuoc Van
authors.initials: TV
authors.lastname: Chu
authors.forename: Marine
authors.initials: M
authors.lastname: Combe
authors.forename: Xavier
authors.initials: X
authors.lastname: Mari
authors.forename: Minh Ngoc
authors.initials: MN
authors.lastname: Nghiem
authors.forename: Thuy Thanh
authors.initials: TT
authors.lastname: Nguyen
authors.forename: Thu The
authors.initials: TT
authors.lastname: Pham
authors.forename: Olivier
authors.initials: O
authors.lastname: Pringault
authors.forename: Emma
authors.initials: E
authors.lastname: Rochelle-Newall
authors.forename: Jean-Pascal
authors.initials: JP
authors.lastname: Torréton
authors.forename: Huy Quang
authors.initials: HQ
authors.lastname: Tran
mesh_terms: D005618:Fresh Water / Q000032:analysis / Q000821:virology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012623:Seawater / Q000032:analysis / Q000821:virology*; D012965:Sodium Chloride / Q000032:analysis; D014744:Vietnam; D017735:Virus Latency; D018406:Virus Physiological Phenomena; D014780:Viruses / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D012965:Sodium Chloride